# Refraction of light and Snell's Law

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##### Intros
###### Lessons
1. Refraction of Light
2. Introduction to refraction, key terms
3. Laws of refraction
4. Optically dense medium
5. Steps to solve refraction problems
##### Examples
###### Lessons
1. A ray of light is traveling from water to diamond. The refractive index of water is 1.33 and that of diamond is 2.42.
1. Which medium is optically denser medium?
2. Compare the angle of incidence to the angle of refraction.
3. What happens to the speed of light as it goes from water to diamond?
1. A beam of light strikes a sheet of glass at an angle of 60°. Find the angle of refraction.
1. A ray of light incident upon a piece of diamond and gets refracted with an angle of 22°. What is the angle of incidence?
1. Find the speed of light in glass.
###### Topic Notes

In this lesson, we will learn:

• Key terms in refraction
• Ray diagrams in refraction
• Solving Snell’s law problems

Notes:

Refraction of light: Bending of light as it strikes the surface of separation of two media.

Key terms

• Incident ray: The incoming ray of light
• Refracted ray: The transmitted ray of light into another medium
• Medium of incidence: The medium in which light travels before it strikes the boundary.
• Medium of refraction: The medium through which refracted ray travels.
• Point of incidence: The intersection of the incident ray and the boundary.
• Normal: An imaginary line is drawn perpendicular to the boundary at the point of incidence.
• Angle of incidence (< $i$ ): The angle between the NORMAL and the incident ray.
• Angle of refraction (< $r$): The angle between the NORMAL and the refracted ray.
• If the incident ray is perpendicular to the boundary the angle of incidence is ZERO, and the angle of refraction will also be ZERO.
• Snell’s law: The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, “n”

• $\large n = \frac{sin \, \theta _{i} }{sin \, \theta _{r}},$

n” is called the index of refraction

In the more general cases the Snell’s law can be written as :

$n _{i} \, sin \, \theta _{i} = n _{r} sin \, \theta _{r}$

$n _{i}$ = medium of inidence refractive index

$n _{r}$ = medium of refraction refractive index

• Index of refraction: Physical characteristics of matter which determines the extent to which light gets refracted.
• Optically dense medium: The medium in which the angle between the ray and normal is smaller is called the optically denser medium.
• The denser the medium the smaller the speed of light in that medium
• The denser the medium the bigger the value of “$n$”.
• The refracted ray bends TOWARDS the normal in optically denser medium

$n$ (index of refraction) $= \frac{C (speed \,of\, light \,in \,air)} {V(speed \, of \, light \, in \, medium)}$, $\quad n = \frac{C}{V}$